Thesis (M.S.) -- Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.

Une analyse détaillée des propriétés physico-chimiques des nanoparticules (NP) anthropogéniques est nécessaire pour comprendre à un niveau mécanistique leurs interactions/toxicité potentielle avec/envers les composants biotiques des systèmes aquatiques naturels. Une telle analyse est également requise pour réaliser une évaluation complète et une optimisation de la performance des méthodes d’(ultra)filtration développées pour circonscrire le relargage des NPs dans les milieux aquatiques. Dans ce contexte, l'objectif de cette thèse de doctorat était de déchiffrer les processus physico-chimiques fondamentaux régissant la capture de nanodendrimères carboxylés (PAMAM-COOH) - utilisés fréquemment dans des applications biomédicales – par des films multicouches du type (poly(diallyldiméthylammonium)chlorure-poly(acide acrylique))n ((PDADMAC-PAA)n) assemblés par déposition séquentielle des composantes polymériques cationique et anionique. À cette fin, une étude systématique des propriétés électrohydrodynamiques des NPs PAMAM-COOH a d'abord été effectuée en fonction du pH et de la concentration en sel monovalent du milieu. Sur la base de la théorie électrocinétique de particules molles ayant une fonctionnalité zwitterionique, il est démontré que les caractéristiques électriques interfaciales des NPs considérées sont déterminées à la fois par des contributions électrostatiques de surface et volumique des nanoparticules, lesquelles dependent de l’extension intraparticulaire de la double couche électrique. L’existence de ces deux types de contributions conduit à un changement remarquable de signe de la mobilité des NPs en modifiant la concentration du sel monovalent en solution et à une dépendance prononcé du point de zéro mobilité des NPs avec la concentration de l’électrolyte. En outre, une confrontation quantitative entre résultats expérimentaux et théorie souligne comment les modifications structurales des NPs induites par des changements de pH et de salinité affectent les caractéristiques électrocinétiques des dendrimères. Dans une deuxième partie, la structure, la morphologie et les propriétés mécaniques des films PDADMAC-PAA et leur évolution temporelle dans des conditions de vieillissement naturel ou après traitement thermique ont été déterminées par microscopie à force atomique (AFM) et analyses microspectroscopie Raman. Les résultats démontrent que les films multicouches PDADMAC-PAA de type exponentiel présentent des caractéristiques mécaniques et structurelles typiques de films polyélectrolytes multicouches à croissance linéaire. En particulier, leur relaxation lente vers un état d’équilibre est accélérée après traitement thermique à 60°C et se révèle être intimement liée à l'instabilité de domaines de films riches en PDADMAC, épuisés en eau (faits confirmés par la théorie de la fonctionnelle de la densité) et marqués par la présence de structures caractéristiques en forme de ‘donuts’. Dans une dernière partie, des résultats préliminaires sont donnés pour la dépendance de l'élasticité des films multicouches PDADMAC-PAA avec la concentration en solution de nanodendrimères. Les résultats suggèrent que ces films multicouches complexes constituent une option prometteuse pour la capture et l'élimination de nanodendrimères carboxylés présents en milieux aqueux / A detailed analysis of the physicochemical properties of engineered nanoparticles (NPs) is required to understand on a mechanistic level their interactions/potential toxicity with/towards biotic components of fresh water systems. Such an analysis is further mandatory to achieve a comprehensive evaluation and optimisation of the performance of (ultra)filtration methods developed to prevent NPs release into aquatic media. Within this context, the aim of this PhD thesis was to decipher the basic physico-chemical processes governing the loading of carboxylated-poly(amidoamine) (PAMAM-COOH) nanodendrimers -commonly employed in biomedical applications- into layer-by-layer assembled (poly(diallyl dimethyl ammonium) chloride-poly(acrylic acid))n ((PDADMAC-PAA)n) multilayer films. For that purpose, a systematic investigation of the electrohydrodynamic properties of PAMAM-COOH NPs was first performed as a function of pH and monovalent salt concentration in solution. On the basis of advanced electrokinetic theory for soft particles with zwitterionic functionality, it is demonstrated that the interfacial electrostatic features of the considered NPs are determined both by surface and bulk particle contributions to an extent that depends on electrolyte concentration. This leads to a remarkable NPs mobility reversal with changing monovalent salt concentration and to a marked dependence of the point of zero NPs mobility on electrolyte content. In addition, confrontation between experiments and theory further highlights how pH- and salt-mediated modifications of the NP particle structure affect dendrimer electrokinetic features at large pH and/or low salt concentrations. In a second part, the structure, morphology and mechanical properties of PDADMAC-PAA films, and their evolution over time under natural aging conditions or after thermal treatment, were addressed from atomic force microscopy (AFM) and Raman microspectroscopy analyses. Results evidence that PDADMAC-PAA multilayer films of exponential type exhibit mechanical and structural features that are typical for polyelectrolyte multilayer films with linear growth. In particular, their slow relaxation to equilibrium is accelerated after heating treatment at 60°C and, in line with density functional theory computation, this relaxation dynamics is shown to be intimately connected to instability of film domains rich in PDADMAC, depleted in water and marked by the presence of characteristic donut-like structures. In a final part, the reported dependence of PDADMAC-PAA multilayer films elasticity on concentration of nanodendrimers in bulk solution suggests that these complex multilayer films constitute a promising option to be further investigated for the loading and removal of carboxylated nanodendrimers from aqueous environments

Microfluidics refers to manipulation, precise control, and behavior of fluids at the micro and nanoliter scales. It has entered the realm of science as a way to precisely measure or mix small amounts of fluid to perform highly controlled reactions. Glass and polydimethylsiloxane (PDMS) are common materials used to create microfluidic devices; however, glass is difficult to process and PDMS is relatively hydrophobic. In this study, SU-8, an epoxy based (negative) photoresist was used to create various electrokinetic microfluidic chips. SU-8 is commonly used in microelectromechanical design. Spin coating of various SU-8 formulations allows for 1 μm to 100 μm thick layers with aspect ratios reportedly as high as 50:1. Case studies were performed to understand the curing/crosslinking process of SU-8 by differential scanning calorimetry. Supplier (MicroChem) recommended parameters were then altered to allow for adequate development of microfluidic channels, while maintaining enough molecular mobility to subsequently bond the SU-8 to a secondary substrate. Three SU-8 layers were used to create fully (SU-8) enclosed microfluidic channels. An (1) SU-8 2050 fully cured base layer was used as a platform on silicon to build from, (2) an SU-8 2050 partially cured layer for developing microfluidic channels , and (3) an SU-8 2007 uncured layer for bonding a secondary substrate to enclose the microfluidic channels. Bond quality was verified by optical and scanning electron microscopy, which resulted in a nearly 100% bond with little to no reflow of SU-8 into channels. Working pressures (ΔP across the capillary) of 15.57 lb/in2 (max detection) were obtained with no fluid leaks. Electroosmotic flow and steaming potential measurements failed. Electrophoretic behavior of glass particles was observed and particle velocities were compared by the application of 200 volts and 300 volts, across a channel length of 2 cm. Particle velocities obtained ranged from 100 μm/s to 1500 μm/s.

Organic materials are ubiquitous in the geologic environment, and can exert significant influence over the interfacial properties of minerals. However, due to the complexity in their structure and interaction with soil solids, their impact has remained relatively unquantified. This study investigated the engineering behaviors of organoclays, which were synthesized in the laboratory using naturally occurring clay minerals and quaternary ammonium compounds of controlled structure and density of loading. Organic cations were chosen to study the effects of functional group structure and size. The laboratory investigation showed that the presence of the organic cations on the mineral surfaces led to increased hydrophobicity of all clays tested. Conduction studies on the electrical, hydraulic, and thermal properties of the organoclay composites suggested that increasing the total organic carbon content resulted in decreased electrical and thermal conductivity, but increased hydraulic conductivity, due to the reduced swelling of the base clay mineral phase. Electrokinetic properties of the organoclays illustrated that compared with the clay's naturally occurring inorganic cations, exchanged quaternary ammonium cations were more likely bound within a particle's shear plane. Consequently, organoclays had less negative zeta potential than that of unmodified bentonite. Increasing the length of one carbon tail was more effective at binding organic cations within the shear plane than increasing the size of the cation, when compared on the basis of total organic carbon content. In terms of large strain strength, the modified organic clays exhibited increased shear strength, in part owing to the reduction in water content caused by the presence of the hydrophobic organic layering. Shear strength increased with single carbon tail length or with cation size, although the latter effect tended to reach a plateau as the length of the four short cation tails increased from 2 to 4. In terms of small strain behavior, the shear modulus was shown to be a function of the total organic carbon content. It is believed that number of particle contacts increased as the organic carbon content increased. Stiffness increased as either the size of the cation or the total organic carbon content was increased. Damping also increased as the organic loading was increased, with the organic phase acting as an energy dissipation mechanism.

Le colmatage membranaire demeure l’un des verrous majeurs des bioréacteurs à membrane (BAM). Ces travaux visent à apporter une contribution à la compréhension de la dynamique de structuration de dépôts complexes formés lors de la filtration frontale de (bio)fluides et son impact sur les performances de filtration. Pour cela, différents outils permettant la mesure in-situ des propriétés structurelles locales des dépôts ont été utilisés de manière à pouvoir relier ces propriétés aux performances globales de filtration. Les propriétés électrocinétiques des dépôts ont également été étudiées. Deux méthodes, l’une optique et l’autre acoustique, ont été utilisées pour caractériser les propriétés structurelles locales des dépôts (épaisseur, cinétique de croissance). Dans un premier temps, les épaisseurs obtenues par les méthodes optiques et acoustiques ont été comparées. Il a été montré que, dans le cas de dépôts peu poreux, les deux méthodes conduisent aux mêmes épaisseurs de dépôts. Dans le cas de dépôts plus poreux, ces deux méthodes permettent l’obtention de données complémentaires à deux niveaux de profondeur différents au sein du dépôt. L’influence des conditions opératoires sur la structuration de dépôts de particules modèles a ensuite été étudiée. Grâce à la méthode optique il a été montré que, quelles que soient les conditions opératoires, il existe une variation temporelle des propriétés du dépôt. De plus, une répartition non homogène du dépôt à la surface de la membrane peut également exister, favorisée par de faibles répulsions entre particules. Enfin, l’applicabilité des différentes méthodes au cas des biofluides issus de BAM a été évaluée. La structure de dépôts complexes constitués lors de la filtration de ces biofluides a ensuite été étudiée. La compressibilité des dépôts, mise en évidence à l’échelle globale par suivi des performances de filtration, a également été observée à l’échelle locale : l’épaisseur du dépôt décroît avec une augmentation de la PTM. De plus, à l’échelle locale, une variabilité spatiale des propriétés du dépôt a été mise en évidence. Afin de contrôler la compressibilité des dépôts l’impact de l’ajout de particules au sein du biofluide a été évalué / Membrane fouling is one of the major drawbacks of membrane bioreactors. This study is thus a contribution to the understanding of the dynamic structuring of complex deposits build-up during dead-end filtration of complex biofluids. Several tools were used to perform in-situ characterization of cake layer structural properties at local scale and to link them to global filtration performances. The electrokinetics properties of the deposit were also investigated. An optical and an acoustic method were used to measure local cake thickness and growth kinetics. The thicknesses given by the two methods were first compared. It was shown that for compact deposits the two different methods lead to the same thickness of the deposit. For more porous deposits, these two methods allow to obtain complementary data at two different depths of the deposits. The influence of operating conditions on cake layer structuring during filtration of modelled particles was evaluated. Using the optical method it was shown that, whatever the operating conditions, the cake structure is not constant in time. Furthermore, a spatial variability of the cake layer thickness might exist especially in the case of weak particle-particle repulsion. Finally, it has been investigated whether the different methods could be applied or not to the case of biofluid filtration. The structural properties of the complex deposits built up during diluted activated sludge filtration were investigated. Cake compressibility was observed at global scale by a monitoring of process performances and was also observed at local scale: cake thickness decreases as TMP increases. Furthermore, at local scale, a spatial variability of deposit structure was found. Particle addition into the biofluid was assessed in order to mitigate compressibility effects

Le coefficient d'électrofiltration est simulé par méthode Lattice Boltzmann dans un chenal 2-D sur une grande gamme de salinité. L'influence de la permittivité et de la viscosité est discutée. La validité de l'équation d'Helmholtz Smoluchowski à de forts potentiels zeta est évaluée. Un modèle de conductivité intrinsèque est développé en prenant en compte les variations locales de conductivité, qui ont un impact significatif en la présence d'espèces polyvalentes. Étendu aux conditions non saturées, l'algorithme montre que la densité de charge électrique associée à l'interface eau-air est une composante clé. Le coefficient présente une attitude non monotone, avec une augmentation par rapport à l'état saturé. L'amplitude de cette augmentation dépend de l'état dynamique des bulles, mobiles ou piégées. L'aspect transport multiphasique est complété par une étude numérique de l'impact de la forme des échantillons sur la mesure des lois reliant saturation et pression capillaire en hydrologie. / The electrokinetic coefficient is simulated in a large range of salinities using the Lattice Boltzmann method in a 2-D channel. The effect of permittivity and viscosity is discussed. The validity of the Helmholtz Smoluchowski equation using strong zeta potentials is assessed. A model of bulk fluid conductivity is derived, taking into account the local variations of conductivity which have a significant impact in the presence of polyvalent counterions. Extended to unsaturated conditions, the model shows that the electrical charge density associated to the air-water interface is a key component. The coefficient shows a non monotonous behaviour, with an enhancement compared to the saturated state. The magnitude of this enhancement depends on the dynamic state of the bubbles, moving or entrapped. The multiphase transport aspect is associated to a numerical study of the influence of the sample geometry on the measurement of the capillary pressure / saturation relationships used in hydrology.

<p>A microfluidic device capable of drug delivery to multiple wells in a concentration gradient was designed for automated high content and high throughput screening. The design was proposed to utilize a nanoporous polycarbonate membrane to spatially and temporally control drug dosage from the microchannels below to the wells above. Microchannels were to hold to the drugs or reagents, while wells were to culture cells. An array of 16 wells was to fit in the equivalent area of a single well of a 96 well plate. Two simpler devices were created to validate electrokinetic drug delivery to a single well and to characterize cell proliferation and viability in micro-wells. The first device tested drug delivery to a single well with methylene blue dye at applied voltages of 100V, 125V, and 150V. It was validated that the dosage of dye could be controlled by increasing the voltage and by increasing the duration the voltage was applied. The second devices were a series of 9-well arrays, each testing a different diameter (1.2 mm – 0.35 mm). These devices were cultured with MCF-7 breast cancer cells over 5 days. At the end of the 5 day study, all diameters except for 0.5 mm and 0.35 mm measured a cell viability of 99% and exhibited cell growth patterns similar to coverslip glass controls. The proposed integrated cell culture and drug delivery device could have application towards early stage drug discovery and could have compatibility with lab equipment originally designed for well plates.</p> / Master of Applied Science (MASc)

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Today, the growing and aging population, and the rise of new global threats on human health puts an increasing demand on the healthcare system and calls for preventive actions. To make existing medical treatments more efficient and widely accessible and to prevent the emergence of new threats such as drug-resistant bacteria, improved diagnostic technologies are needed. Potential solutions to address these medical challenges could come from the development of novel lab-on-chip (LoC) for point-of-care (PoC) diagnostics. At the same time, the increasing demand for sustainable energy calls for the development of novel approaches for energy conversion and storage systems (ECS), to which micro- and nanotechnologies could also contribute. This thesis has for objective to contribute to these developments and presents the results of interdisciplinary research at the crossing of three disciplines of physics and engineering: electrokinetic transport in fluids, manufacturing of micro- and nanofluidic systems, and surface control and modification. By combining knowledge from each of these disciplines, novel solutions and functionalities were developed at the macro-, micro- and nanoscale, towards applications in PoC diagnostics and ECS systems. At the macroscale, electrokinetic transport was applied to the development of a novel PoC sampler for the efficient capture of exhaled breath aerosol onto a microfluidic platform. At the microscale, several methods for polymer micromanufacturing and surface modification were developed. Using direct photolithography in off-stoichiometry thiol-ene (OSTE) polymers, a novel manufacturing method for mold-free rapid prototyping of microfluidic devices was developed. An investigation of the photolithography of OSTE polymers revealed that a novel photopatterning mechanism arises from the off-stoichiometric polymer formulation. Using photografting on OSTE surfaces, a novel surface modification method was developed for the photopatterning of the surface energy. Finally, a novel method was developed for single-step microstructuring and micropatterning of surface energy, using a molecular self-alignment process resulting in spontaneous mimicking, in the replica, of the surface energy of the mold. At the nanoscale, several solutions for the study of electrokinetic transport toward selective biofiltration and energy conversion were developed. A novel, comprehensive model was developed for electrostatic gating of the electrokinetic transport in nanofluidics. A novel method for the manufacturing of electrostatically-gated nanofluidic membranes was developed, using atomic layer deposition (ALD) in deep anodic alumina oxide (AAO) nanopores. Finally, a preliminary investigation of the nanopatterning of OSTE polymers was performed for the manufacturing of polymer nanofluidic devices. / <p>QC 20140509</p> / Rappid / NanoGate / Norosensor